The Arctic Ocean is rapidly changing. Air temperature is rising two to four times faster in the Arctic than the global average, with dramatic consequences for the ecosystems. Polar zooplankton species have to cope with those increasing temperatures, whilst simultaneously facing increasing competition by boreal-Atlantic sister species advected into the Arctic Ocean via a stronger Atlantic inflow. To assess the sensitivity of Arctic and Atlantic zooplankton to rising temperatures, respiration rates of dominant Arctic species (Calanus hyperboreus, Calanus glacialis, Paraeuchaeta glacialis, Themisto libellula) and their co-occurring Atlantic congeners (Calanus finmarchicus, Paraeuchaeta norvegica, Themisto abyssorum) were measured at ambient temperatures and simulated conditions of ocean warming from 0 to 10°C during three expeditions with RV Polarstern to the Arctic Fram Strait. Arctic zooplankton showed only slowly increasing respiration rates with increasing temperatures, also indicated by low Q₁₀ ratios. In contrast, boreal-Atlantic representatives responded to higher temperatures by a rapid and steeper increase in their respiration rates (higher Q₁₀), suggesting higher metabolic activity. These results imply that Arctic species are physiologically more tolerant to ocean warming than expected but might be outcompeted by their Atlantic congeners beyond a certain temperature threshold in areas of strong distribution overlap. Thus, the ‘Atlantification’ of the Arctic zooplankton community seems to be driven rather by ecological interactions than by physiological limitations. Changes in zooplankton community composition and biodiversity will have major consequences for trophodynamics and energy flux in Arctic ecosystems, since polar species tend to be larger than their southern counterparts and have a higher lipid content, providing more energy-rich food for higher trophic levels.

北冰洋正在迅速变化。北极的气温上升速度是全球平均水平的两到四倍，对生态系统产生了巨大的影响。极地浮游动物物种必须应对这些不断升高的温度，同时面临通过更强的大西洋流入平流进入北冰洋的北方-大西洋姐妹物种日益激烈的竞争。为了评估北极和大西洋浮游动物对气温上升的敏感性，北极优势物种的呼吸速率（水葫芦,冰壶,冰副藻,蝾螈) 和它们同时出现的大西洋同系物 (凤仙花,褐副藻,Themisto abyssorum) 在环境温度下测量，并在 RV 的三次探险期间模拟海洋变暖从 0°C 到 10°C 的条件极地船到北极弗拉姆海峡。北极浮游动物仅表现出随着温度升高而缓慢增加的呼吸速率，低 Q ₁₀比率也表明了这一点。相比之下，北方 - 大西洋代表通过呼吸速率的快速和急剧增加（更高的 Q ₁₀)，表明更高的代谢活性。这些结果表明，北极物种在生理上对海洋变暖的耐受性比预期的要强，但在分布强烈重叠的区域，它们的大西洋同系物可能会在超过一定温度阈值时被其竞争。因此，北极浮游动物群落的“大西洋化”似乎是由生态相互作用而非生理限制驱动的。浮游动物群落组成和生物多样性的变化将对北极生态系统的营养动力学和能量通量产生重大影响，因为极地物种往往比其南部同类更大，脂质含量更高，为更高的营养水平提供更多能量丰富的食物。